\(\displaystyle 1).\;\; \frac{1}{2}-\frac{1}{3\times 1!}+\frac{1}{4\times 2!}+\cdots\)
\(\displaystyle 2).\;\; \frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+\frac{1}{2^4}+\cdots\)
\(\displaystyle 3).\;\; \frac{1}{2.3} +\frac{1}{4.5}+\frac{1}{6.7} +\cdots\)
\(\displaystyle 4).\;\; \frac{1}{3}+\frac{1}{4}.\frac{1}{2!} +\frac{1}{5}.\frac{1}{3!}+\cdots\)
\( \displaystyle 5).\;\; \sum_{n=1}^{\infty} \frac{(-1)^{n+1}}{n(n+1)}\)
\( \displaystyle 6).\;\; \sum_{n=1}^{\infty} \frac{n^2-n+1}{n!}\)
\(\displaystyle 7).\;\; \frac{1}{5}+\frac{1}{3}.\frac{1}{5^3}+\frac{1}{5}.\frac{1}{5^5}+\cdots\)
\(\displaystyle 8).\;\; \frac{4}{20}+\frac{4.7}{20.30}+\frac{4.7.10}{20.30.40}+\cdots\)
\(\displaystyle 9).\;\; \sum_{n=0}^{\infty} \frac{5n+1}{(2n+1)!}\)
\(\displaystyle 10).\;\; \sum_{n=1}^{\infty} \frac{(-1)^n}{n(n+1)}\)
\(\displaystyle 11).\;\; \sum_{n=1}^{\infty} \frac{1}{(2n+1)^2}\)
\(\displaystyle 12).\;\; \frac{1}{1!}+\frac{1+2}{2!}+\frac{1+2+3}{3!}+\cdots\)
\(\displaystyle 13).\;\; \sum_{n=1}^{\infty} \frac{1}{(2 n-1)^{2}}\)
\(\displaystyle 14).\;\; \sum_{n=1}^{\infty} n\left(\frac{1}{2}\right)^{n}\)
\(\displaystyle 15).\;\; \sum_{n=2}^{\infty} \frac{(-1)^{n}}{n^{2}+n - 2}\)
\(\displaystyle 16).\;\; \frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\cdots+\frac{1}{100.101}\)
\(\displaystyle 17).\;\; \sum_{n=1}^{\infty}(-1)^{n+1} \frac{(n+1)^{2}+1}{(n+1) n !}\)
\(\displaystyle 18).\;\; \sum_{n=0}^{\infty} \frac{1}{(n+2) n!}\)
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